From: Timo Kokkonen <timo.t.kokkonen@iki.fi>
Date: Mon, 30 Sep 2013 18:09:07 +0000 (+0300)
Subject: main: Fix busy loop with reading
X-Git-Url: http://git.itanic.dy.fi/?p=log-plotter;a=commitdiff_plain;h=9719680d66d26ab962426dc75672f0f9d049ba18

main: Fix busy loop with reading

As the baud.c opens the serial device with O_NBLOCK flag, read will
just return immediately when there is nothing to read. That basically
makes the read loop a a busy loop, consuming one CPU core fully at all
times.

Fix the problem by using epoll to wait until something becomes
available on the serial port to read.

Signed-off-by: Timo Kokkonen <timo.t.kokkonen@iki.fi>
---

diff --git a/main.c b/main.c
index b4a4c8f..847a110 100644
--- a/main.c
+++ b/main.c
@@ -1,11 +1,14 @@
 #include <stdio.h>
 #include <unistd.h>
+#include <sys/epoll.h>
 
 #include "baud.h"
 
 int main(int argc, char *argv[])
 {
+	struct epoll_event ev;
 	int fd, baud, ret;
+	int epoll_fd;
 	char *device;
 	char buf[256];
 
@@ -27,16 +30,31 @@ int main(int argc, char *argv[])
 		return 1;
 	}
 
+	epoll_fd = epoll_create(1);
+
+	ev.events = EPOLLIN;
+	ev.data.fd = fd;
+	if (epoll_ctl(epoll_fd, EPOLL_CTL_ADD, fd, &ev) == -1) {
+		perror("epoll_ctl");
+		return 1;
+	}
+
 	while (1) {
+		ret = epoll_wait(epoll_fd, &ev, 1, -1);
+		if (ret == 0)
+			continue;
+
+		if (ret < 0) {
+			perror("epoll");
+			return 1;
+		}
+
 		ret = read(fd, buf, sizeof(buf));
 		if (read < 0) {
 			perror("read");
 			break;
 		}
 
-		if (read == 0)
-			break;
-
 		ret = write(1, buf, ret);
 		if (read < 0) {
 			perror("write");